Diesel engines are used in a variety of different applications, such as school buses, trucks, generator sets, marine equipment and industrial equipment. Gasoline engines are also used in a variety of different applications, perhaps the most well-known and widespread of such uses being for motor vehicles, such as cars and trucks. If fuel systems are timed properly, economic benefits, such as less fuel consumption and longer lasting engine parts, and environmental benefits, such as cleaner engine emissions, are possible.
In the past, some engines were timed using an intrinsic built-in timing pin. Typically, as for instance in the Cummins midrange diesel engines, the timing pin is located on the front gear housing under the fuel pump, which is in a separate housing. Using this method, the timing pin slides into the camshaft gear in locating the piston positioned at top dead center. Because the timing pin is located in a separate housing in the engine, it is difficult to be precise when locating top dead center of the piston. Furthermore, because the typical current midrange engines have the accessory drive located beneath the fuel pump, it has become more difficult to gain access to the timing pin. Another disadvantage of the timing pin method is that it allows for a great opportunity of operator error in locating top dead center. This error can be caused if the timing pin is only slightly out of alignment with its access hole to the camshaft gear. Changing emission laws, costs of fuels and the demands on the engine have also made engine timing a more critical specification than it has been in the past. Based upon these disadvantages, it is currently extremely difficult and inefficient to use the timing pin method.
Another method for determining top dead center is the "positive stop" method. The "positive stop" method, if not performed correctly, involves a risk of severe engine damage. This engine damage can be caused if a large amount of torque is created when the valve contacts the piston. The torque in combination with the valve-piston contact can easily cause the valve to bend or become otherwise disfigured or to cause a push tube to bend. Furthermore, this method is not always accurate in determining top dead center. Using the positive stop method on a diesel engine, one would turn the engine piston to approximate top dead center on the number one cylinder, and then remove all fuel lines from the fuel pump and fuel injectors. After all of the fuel lines have been removed, the fuel injectors must be removed. Removal of the fuel lines and the fuel injectors can be a very time consuming process. The next step involves running the rocker adjustment screw down until there is no lash between the rocker lever and the valve stem on said cylinder number one. The rocker adjustment screw is then rotated until the valves are close to hitting the pistons. The engine is then turned until the piston has made contact with the valve. At this point, there is a possibility of bending or disfiguring the valve or bending a push tube if too much torque is created between the piston and the valve. A pointer is then installed on the front cover of the engine to reference the crank shaft to this position. The engine is then rotated in the opposite direction until the engine "locks down" or until the piston again contacts the valve causing the engine rotation to stop. There is also a potential for bending or disfiguring the valve or bending a push tube at this point in the process. The halfway point between this mark and the mark on the pointer when installed is top dead center. Using the "positive stop" method, the engine must then be reassembled and the valve lash adjusted before timing the fuel pump. These final tasks are very time consuming in and of themselves. These potential problems in the current practices of determining absolute top center have also dictated that a more efficient and simple way to determine absolute top dead be developed.
There are some devices which have been designed with the object of determining top dead center of a piston. Many of these designs use a variety of gauges to measure the movement of the piston in determining top dead center. These gauges typically access the piston through holes created by removed spark plugs or removed fuel injectors. In the apparatus for measuring piston position described in U.S. Pat. No. 3,765,098 issued to Schafer, Sr., a gauge indicator is placed directly on the piston by access means through a hole created by a removed spark plug. As the piston is displaced within the bore, the spindle is displaced on the gauge to develop readings indicative of the piston position. Other types of gauge indicators, such as those described in U.S. Pat. No. 3,744,142 issued to Marshall and U.S. Pat. No. 1,737,726 issued to Muzyn, describe devices which place gauge devices directly onto the pistons through a hole created by an absent spark plug. Although these type devices can provide accurate measurements for top dead center, there is a potential for error introduced by having to access the piston with a gauge through a hole that is created by a displaced spark plug. These devices also require the user to remove a spark plug completely in order to gain access to the piston. This step also includes the potential for damaging the spark plug during removal or during replacement after the timing is completed. These methods also do not take into account or measure for the lash in the crank shaft which is typically present during the piston's operation. Essentially, the methods which are known in the art only determine the top dead center of the piston. It is known in the art that, in normal operation of an internal combustion engine, the piston is at the top dead center during a period called the "piston duration." However, the crank shaft is at top dead center only at the mid-point of the piston duration. The prior art contains devices which locate top dead center of the piston in the piston duration, but not necessarily at the point where the crank shaft is also at top dead center.
Accordingly, there is a need for a timing apparatus which provides little chance for engine damage in use, does not require access to the piston via a hole created by removal of a spark plug or a fuel injector, and maximizes the efficiency of an engine by precisely determining top dead center of the piston and crank shaft so that the engine can be properly timed.